Subject: Re: Stalls when starting a VSOCK listening socket: soft lockups, RCU stalls, timeout

From: Thomas Gleixner <[email-masked]>
Date: Tue, 10 Mar 2026 14:47:35 +0100

On Tue, Mar 10 2026 at 14:40, Matthieu Baerts wrote:
> On 10/03/2026 13:28, Thomas Gleixner wrote:
>
> (...)
>
>> I've updated the debug patch and removed the @users conditionals so it
>> keeps searching. So it should find that magic 73.
>
> It looks like it does, thank you! I just tried this new debug patch, and
> I managed to boot 100 times without issues, while before I was getting
> it after max 20 attempts. I left the test running to boot up to 1000
> times, just in case.

Now that I actually understood the problem, I was able to write a
reproducer which triggers the issue 100% reliable.

The debug patch does cure it and it does the right thing. I have a
better version of that in testing right now which avoid all that flaky
accounting and especially in the vfork() case the full tasklist walk.
I'll send out a complete patch series with changelogs etc. later.

Thanks a lot for your patience and invaluable help. Very appreciated!

        tglx